A chronograph is used by target shooters and others to measure the velocity of a bullet as it is discharged from the muzzle of a firearm. Muzzle velocity is deemed an important criterion in the shooting art and is taken into account when aiming or sighting the firearm as well as when loading and/or selecting ammunition. Since muzzle velocity is subject to the many vagaries of each particular firearm and ammunition load, it is beneficial to the shooter to have means for making a rapid and accurate determination of muzzle velocity in the field for each shooting situation.
Modern chronographs commonly employ a Doppler radar technique to determine muzzle velocity; as evidenced by Storm, U.S. Pat. No. 2,524,610. Basically, they sample the bullet velocity along a portion of its trajectory and extrapolate in reverse to make a calculated estimate of the bullet's velocity at the muzzle. Naturally, the closer to the muzzle the velocity sampling is taken the less likely the velocity will have been influenced by extraneous error factors. However, the ability of prior art chronographs to get a sampling in near proximity to the muzzle has been limited by the following factors.
Chronographs which employ radar techniques are under the jurisdiction of the Federal Communications Commission and are classified as "Field Disturbance Sensors". These devices are severely limited in their power output by 47 Code of Federal Regulations, Part 15, Subpart F.
If a conventional radar-type chronograph is placed in near proximity to the muzzle where it can obtain a reading of true muzzle velocity, its low power output will result in a return signal that is masked by the noise caused by the sonic and electromagnetic disturbances associated with the firearm blast. The sonic disturbance will cause vibratory excursions of the radar antenna that distort the return signal, and the electromagnetic disturbance will obscure the return signal in noise. Thus prior art chronographs have of necessity sampled the bullet velocity downrange from the muzzle, but only after spurious influences on the bullet velocity have been introduced.
The foregoing reasons explain the limitations of the chronograph measurement art to date and define a problem whose solution is an objective of the present invention.